The present invention relates to a process for alkane and/or cycloalkane isomerization in the presence of feed impurities.
The use of supported platinum catalysts (such as platinum on a zeolite) for isomerizing saturated hydrocarbons, in particular normal alkanes to isoalkanes (such as n-pentane to isopentane), is well known. Impurities, in particular sulfur compounds, which are present in the feed can cause a rapid decrease in catalyst activity. Pretreatment of the feed prior to the isomerization to remove a major portion of these impurities is one option to alleviate or eliminate this catalyst deactivation, but this route is expensive because additional equipment and operating costs are required. Also, the levels of these impurities in the feed may fluctuate, and pretreatment of the feed may not always be adequate. Another option to alleviate the deactivation of isomerization catalysts by sulfur impurities is to operate the isomerization processes at relatively high hydrogen to hydrocarbon ratios and at relatively high temperatures. However, this route is also expensive and generally produces undesirably high amounts of by-products, mainly light gases which are formed by hydrocracking of feed hydrocarbons. The present invention is directed to a more effective method of alleviating, and even eliminating, catalyst deactivation problems caused by the presence of sulfur impurities in isomerization feeds which comprises injecting an additive into the feed to counteract detrimental effects caused by these impurities. The amount of the injected additive is generally correlated with the types and levels of sulfur compounds which are present as impurities in the feed so as to alleviate, or even completely eliminate, catalyst deactivating effects caused by these sulfur compounds.